P1335: REPAIR OF DYSFUNCTIONAL BONE MARROW ENDOTHELIAL CELLS ALLEVIATES APLASTIC ANEMIA
Authors: Shu-Qian Tang, Tong Xing, Zhong-Shi Lyu, LI-Ping Guo, MI Liang, Chen-Yuan LI, Yuan-Yuan Zhang, Yu Wang, Lan-Ping Xu, Xiao-Hui Zhang, Xiao-Jun Huang, Yuan Kong
Journal: HemaSphere (2023)

Topic: 23. Hematopoiesis, stem cells and microenvironment Background: Aplastic anemia(AA), regarded as pancytopenia and bone marrow(BM) failure, is thought to be primarily caused by a profound deficit in hematopoietic stem and progenitor cells and abnormally activated immune cells. Recently, increasing evidence suggested that alterations in the BM microenvironment contribute to the process of AA. Endothelial cell(EC), which is a key component of BM microenvironment, plays a crucial role in supporting hematopoiesis and regulating immunity. Our previous studies (Blood2016, Blood2018, AJH2018) confirmed that BM EPCs are important for regulating HSCs and Megakaryocytes. However, it remains unknown whether impaired BM ECs contribute to the occurrence of AA and whether restoring BM ECs could improve hematopoiesis and immune status in AA. Aims: This study aimed to evaluate the number and functions of BM ECs in AA mice and in AA patients. Moreover, we investigated whether the damaged BM ECs are involved in the occurrence of AA and whether EC infusion or NAC treatment could ameliorate hematopoietic failure and immune disorders in AA mice. Furthermore, the effect of NAC on repairing dysfunctional BM ECs derived from AA patients in vitro was detected to provide new insights into the underlying pathogenesis and potential therapy for AA. Methods: A classic AA mouse model was established and VE-cadherin blocking antibody that could selectively inhibits the function of BM ECs without affecting other BM stromal compartments was used to validate the role of BM ECs in the occurrence of AA. N-acetyl-L-cysteine(NAC, a ROS scavenger) treatment, preventative NAC treatment or the exogenous EC infusion was administrated to AA mice. Furthermore, a total of 15 AA patients and 30 age-matched healthy donors (HDs) were enrolled in this study. The functions of BM ECs from AA patients and HDs were evaluated by ROS level, apoptosis, migration and tube formation assays. The coculture experiments of BM CD34+ cells and non-contact coculture or direct-contact coculture experiments of CD3+ cells with BM ECs from HDs or from AA patients treated with or without NAC were performed, respectively. Results: In this study, reduced and dysfunctional BM ECs were observed in AA mice. More importantly, hematopoietic failure and immune imbalance became more severe when the function of BM ECs was antagonized by VE-cadherin blocking antibody, whereas preventative or non-preventative treatment with NAC or EC infusion restored hematopoietic and immunological status by repairing BM ECs in AA mice. Consistently, BM ECs in AA patients were decreased and dysfunctional characterized by markedly higher ROS level, apoptosis ratio and inferior angiogenic ability. Furthermore, defective BM ECs in AA patients impeded hematopoiesis support and dysregulated T cell differentiation towards proinflammatory phenotypes, which could be improved in vitro by NAC, and the non-contact coculture system could better prevent NAC causing inflammatory response by affecting T cells directly. In addition, activated ROS pathway and enriched immune and hemopoiesis associated pathways strongly supported that dysfunctional BM ECs are associated with the occurrence of AA. Summary/Conclusion: Dysfunctional BM ECs with impaired hematopoiesis-supporting and immunomodulatory abilities contribute to the occurrence of AA, suggesting that repairing dysfunctional BM ECs might be a potential therapeutic approach for AA patients. #Shu-Qian Tang and Tong Xing are co-first authors. Keywords: Aplastic anemia, Hematopoietic stem cell, Endothelial cell, T cell